Anode active material, method of preparing the same, and anode and lithium battery containing the material

ABSTRACT

Silicon oxide based composite anode active materials including amorphous silicon oxides are provided. In one embodiment, the amorphous silicon oxide is represented by SiO x  (where 0&lt;x&lt;2), has a binding energy of about 103 to about 106 eV, a silicon peak with a full width at half maximum (FWHM) ranging from about 1.6 to about 2.4 as measured by X-ray photoelectron spectrometry, and an atomic percentage of silicon greater than or equal to about 10 as calculated from an area of the silicon peak. The anode active material is a composite anode active material obtained by sintering hydrogen silsesquioxane (HSQ). Anodes and lithium batteries including the anode active material exhibit improved charge and discharge characteristics.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2007-0001658, filed on Jan. 5, 2007 in the KoreanIntellectual Property Office, the entire content of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to anode active materials, methods ofpreparing the same, and anodes and lithium batteries containing thematerials. More particularly, the invention is directed to anode activematerials having particular silicon peaks as measured by X-rayphotoelectron spectrometry.

2. Description of the Related Art

In an effort to achieve high voltages and energy densities, research anddevelopment has been extensively conducted into non-aqueous electrolytesecondary batteries using lithium compounds as anodes. Specifically,metallic lithium has become the subject of intense research due to itsability to impart high initial battery capacity. Accordingly, lithiumhas gained great attention as a prominent anode material. However, whenmetallic lithium is used as an anode material, large amounts of lithiumare deposited on the surface of the anode in the form of dendrites,which may degrade charge and discharge efficiencies or causeinternal-shorts between the anode and the cathode (positive electrode).Further, lithium is very sensitive to heat or impact and is prone toexplosion due to its instability, i.e., high reactivity, which has heldup commercialization. In order to eliminate these problems with the useof metallic lithium, carbonaceous materials have been proposed for useas anode materials. Carbonaceous anodes perform redox reactions suchthat lithium ions in the electrolytic solution intercalate/deintercalatein the carbonaceous material which has a crystal lattice structureduring charge and discharge cycles. These anodes are referred to as“rocking chair type” anodes.

The carbonaceous anode has made a great contribution to the widespreaduse of lithium batteries by overcoming various disadvantages associatedwith metallic lithium. However, electronic equipment are becomingsmaller and more lightweight, and the use of portable electronicinstruments is becoming more widespread, making the development oflithium secondary batteries having higher capacities a major focalpoint. Lithium batteries using carbonaceous anodes have low batterycapacity because of the porosity of the carbonaceous anode. For example,graphite (which is an ultra-high crystalline material), when used in aLiC₆ structure (made by reaction of graphite with lithium ions), has atheoretical capacity density of about 372 mAh/g. This is only about 10%that of metallic lithium, i.e., 3860 mAh/g. Thus, in spite of manyproblems with conventional metallic anodes, studies for improvingbattery capacity using metallic lithium as the anode material areactively being carried out.

A representative example of such studies is the use of materials thatcan alloy with lithium, e.g., Si, Sn, Al, or the like, as anode activematerials. However, materials that can alloy with lithium, such as Si orSn, may present several problems, including volumetric expansion duringformation of the lithium alloy, creation of electrically disconnectedactive materials in an electrode, aggravation of electrolyticdecomposition, and so on.

In order to overcome these problems with the use of such a metallicmaterial, a technique of using a metal oxide exhibiting a relatively lowvolumetric expansion as an anode active material has been proposed. Forexample, use of an amorphous Sn-based oxide has been proposed whichminimizes the Sn particle size and prevents agglomeration of Snparticles during charge and discharge cycles, thereby leading toimprovement of capacity retention characteristics. However, Sn-basedoxides unavoidably cause reactions between lithium and oxygen atoms,which is responsible for considerable irreversible capacities.

High capacity electrodes using silicon oxides as the anode materials forsecondary lithium ion batteries have also been proposed. However,irreversible capacities are considerably large during initialcharge-discharge cycling stages, giving the secondary lithium ionbatteries undesirable cycling characteristics and preventing practicaluse.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, a silicon oxide basedcomposite anode active material has a particular silicon peak asmeasured by X-ray photoelectron spectrometry.

In another embodiment of the present invention, an anode contains theanode active material. In yet another embodiment, a lithium batteryinclude the anode active material, and the battery exhibits improvedcharge and discharge efficiency and charge and discharge capacity.

In still another embodiment of the present invention, a method ofpreparing the anode active material is provided.

According to an embodiment of the present invention, a silicon oxidebased composite anode active material includes an amorphous siliconoxide represented by the general formula SiO_(x) (where 0<x<2), having abinding energy ranging from about 103 to about 106 eV and a silicon peakwith a full width at half maximum (FWHM) ranging from about 1.6 to about2.4 as measured by X-ray photoelectron spectrometry, and having anatomic % greater than or equal to about 10, as calculated from an areaof the peak.

According to another embodiment of the present invention, an anodecomprises the anode active material. In another embodiment, a lithiumbattery includes the anode active material.

According to another embodiment of the present invention, a method ofpreparing the anode active material includes sintering hydrogensilsesquioxane (HSQ) in an inert atmosphere at a temperature rangingfrom about 900 to about 1300° C.

Unlike conventional anode active materials derived from silicon dioxide,anode active materials according to embodiments of the present inventioninclude amorphous silicon oxide having a novel structure, therebyimproving initial charge and discharge efficiency. In addition, anodesand lithium batteries including the anode active materials of thepresent invention exhibit excellent charge and dischargecharacteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill be better understood by reference to the following detaileddescription when considered in conjunction with the attached drawings inwhich:

FIG. 1 depicts the X-ray diffraction patterns of the anode activematerial powders prepared according to Example 1 and Comparative Example1;

FIG. 2 depicts the results of X-ray photoelectron spectrometry of theanode active materials prepared according to Example 1 and ComparativeExample 2;

FIGS. 3A and 3B depict the electric potential to capacity relationshipduring the first charge and discharge cycle of lithium batteriesemploying the anode active materials prepared according to Example 1 andComparative Example 1; and

FIG. 4 is a cross-sectional view of a lithium battery according to oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A silicon oxide based composite anode active material according to oneembodiment of the present invention includes an amorphous silicon oxiderepresented by the general formula SiO_(x) (0<x<2), having a bindingenergy ranging from about 103 to about 106 eV and a silicon peak with afull width at half maximum (FWHM) ranging from about 1.6 to about 2.4 asmeasured by X-ray photoelectron spectrometry, and having an atomic %greater than or equal to about 10, as calculated from an area of thepeak.

The X-ray diffraction results shown in FIG. 1, indicate that theamorphous silicon oxide has an amorphous phase without a peak forcrystallinity.

In addition, the amorphous silicon oxide (SiO_(x)) according to anembodiment of the present invention has a silicon (Si) atomic % ofgreater than about 10%. In addition, the silicon (Si) has a relativelyhigh binding energy of, e.g., 105.4 eV, as measured by X-rayphotoelectron spectrometry, unlike conventional silicon oxide (SiO).

The Si has a high atomic % and a high binding energy presumably becausethe amorphous silicon oxide (SiO_(x)) according to an embodiment thepresent invention includes a nanopore structure. The amorphous siliconoxide (SiO_(x)) having the nanopore structureintercalates/deintercalates lithium ions highly efficiently compared toconventional silicon oxide.

In one exemplary embodiment, the amorphous silicon oxide (SiO_(x)) has abinding energy ranging from about 105 to about 106 eV as measured byX-ray photoelectron spectrometry, and a Si peak with a full width athalf maximum (FWHM) ranging from about 1.8 to about 2.2.

In another exemplary embodiment, the amorphous silicon oxide (SiO_(x))has the general formula SiO_(x) (where 1<x<1.7). The atomic % of theamorphous silicon oxide (SiO_(x)), calculated from an area of thesilicon peak, is greater than or equal to about 8. In one embodiment,for example, the atomic % ranges from about 8 to about 10.8%.

According to one embodiment, the amorphous silicon oxide (SiO_(x)) maybe prepared by sintering hydrogen silsesquioxane (HSQ). HSQ, representedby the general formula HSiO_(3/2), is a kind of polyhedral oligomericsilsesquioxane (POSS). Before heat treatment, the POSS has a cagestructure, a network structure, or a mixed structure of cage and networkstructures. After heat treatment, the structure of the POSS may betransformed into a network structure. The POSS is a low dielectricmaterial that can prepare mesoporous materials having small pores withspecified diameters using a sol-gel method. In addition, the POSS hasbeen researched as a semiconductor insulator material. However, nomethod of using the POSS as an anode active material has yet beenreported. IN one embodiment of the present invention, a composite anodeactive material contains a new amorphous silicon oxide obtained bydirectly sintering HSQ (that does not have carbon atoms) at a hightemperature of about 900° C.

The HSQ used in preparing the silicon oxide based composite anode activematerial may be obtained by a sol-gel reaction of a silane compound. Inthe sol-gel reaction, a silane compound having low molecular weight issubjected to hydrolysis and condensation under appropriate reactionconditions to obtain a sol having stable and uniformly structuredinorganic particles dispersed therein. Alternatively, a gel may beproduced by additional growth of the inorganic particles of the sol. Inone embodiment of the present invention, HSQ of the general formulaHSiO_(3/2) is obtained by the sol-gel reaction of the silane compound.

The silane compound may be a silane compound represented by Formula (1).HSi(R₁)(R₂)(R₃)  (1)In Formula (1), each of R₁, R₂ and R₃ is independently selected fromhalogen atoms, and substituted and unsubstituted C₁₋₁₀ alkoxy groups.Nonlimiting examples of suitable silane compounds includetrichlorosilane, trimethoxy silane, and triethoxy silane.

The substituted alkoxy group of the silane compound of Formula (1) mayinclude a substituent selected from C₁₋₅ alkyl groups, C₂₋₅ alkenylgroups, and C₁₋₅ alkoxy groups.

In the sol-gel reaction carried out for preparation of HSQ, the silanecompound may be sol-gel reacted with from about 10 to about 60 wt % of acarbonaceous material based on the total weight of the mixture of thesilane compound and the carbonaceous material. Addition of thecarbonaceous material to the sol-gel reaction system yields a compositestructure having the carbonaceous material contained in the HSQ.

When the HSQ having the composite structure is sintered, the siliconoxide based composite anode active material may further comprisecarbonaceous particles dispersed within the amorphous silicon oxide.

In addition, when the HSQ is sintered according to one embodiment of thepresent invention, from about 10 to about 90 wt % of a carbon precursormay be added to the HSQ based on the total weight of the mixture of theHSQ and the carbon precursor. When adding the carbon precursor, thesilicon oxide based composite anode active material may further comprisea carbonaceous coating layer. In other words, a silicon oxide basedcomposite anode active material may further comprise a carbonaceouscoating layer formed on the amorphous silicon oxide. The carbonaceouscoating layer may be formed by entirely coating the amorphous siliconoxide particles.

In another embodiment of the present invention, an anode includes theanode active material. More specifically, an anode according to oneembodiment of the present invention may be manufactured using a siliconoxide based composite anode active material, i.e., a porous anode activematerial.

The anode may be manufactured by, for example, forming a mixed anodematerial including the anode active material and a binder shaping themixed anode material. Alternatively, the mixed anode material may beapplied onto a current collector made of, e.g., copper foil.

More specifically, an anode composition may be prepared and thendirectly coated on a copper foil current collector to prepare and anodeplate. Alternatively, the anode composition can be cast on a separatesupport to form a porous anode active material film, which film is thenstripped from the support and laminated on the copper foil currentcollector, thereby obtaining an anode plate.

The anode of the present invention is not limited to the illustratedexamples and many other modifications may be made within the scope ofthe invention.

To attain higher capacity batteries, large amounts of current arerequired to charge and discharge the higher capacity batteries, whichrequire low resistance materials for the electrode materials. Thus, inorder to reduce the resistance of the electrode, a variety of conductingmaterials are generally employed. Nonlimiting examples of suitableconducting materials include carbon black, and graphite fine particles.

According to another embodiment of the invention, a lithium batteryincludes the above anode. As shown in FIG. 4, the lithium battery 3includes an electrode assembly 4 including a cathode 5, anode 6 and aseparator 7 positioned between the cathode 5 and anode 6. The electrodeassembly 4 is housed in a battery case 8, and sealed with a cap plate 11and sealing gasket 12. An electrolyte is then injected into the batterycase to complete the battery. A lithium battery according to oneembodiment of the present invention may be prepared in the followingmanner.

First, a cathode active material, a conducting agent, a binder, and asolvent are mixed to prepare a cathode active material composition. Thecathode active material composition is coated directly on a metalliccurrent collector and dried to prepare a cathode electrode. In analternative embodiment, the cathode active material composition is caston a separate support body to form an anode active material film, whichfilms is then peeled off the support body and laminated on the metalliccurrent collector.

A lithium-containing metal oxide may be used as the cathode electrodeactive material. Nonlimiting examples of suitable lithium-containingmetal oxides include LiCoO₂, LiMn_(x)O_(2x), LiNi_(x−1)Mn_(x)O_(2x)(where x=1, 2), and LiNi_(1−x−y)Co_(x)Mn_(y)O₂ (where 0≦x≦0.5, 0≦y≦0.5).Specific, nonlimiting examples of suitable lithium-containing metaloxides include compounds capable of oxidizing and reducing lithium ions,such as LiMn₂O₄, LiCoO₂, LiNiO₂, LiFeO₂, V₂O₅, TiS₂, MoS₂, and the like.

Carbon black may be used as the conducting agent. Nonlimiting examplesof suitable binders include vinylidene fluoride/hexafluoropropylene(HFP) copolymers, polyvinylidene difluoride (PVdF), polyacrylonitrile,polymethacrylate, polytetrafluoroethylene, and mixtures thereof. Styrenebutadiene rubber polymers may also be used as the binder. Nonlimitingexamples of suitable solvents include N-methyl-pyrrolidone, acetone,water, and the like. The amount of the cathode electrode activematerial, the conducting agent, the binder, and the solvent used in themanufacture of the lithium battery are amounts generally acceptable inthe art.

Any separator commonly used in lithium batteries can be used in thelithium battery. In particular, an exemplary separator may have lowresistance to migration of ions in an electrolyte and have excellentelectrolyte-retaining ability. Nonlimiting examples of suitableseparators include glass fibers, polyester, polyethylene, polypropylene,polytetrafluoroethylene (PTFE), and combinations thereof. The separatormay be a rollable material in non-woven or woven fabric form. Specificnonlimiting examples of suitable separators for use in lithium ionbatteries include polyethylene, polypropylene and the like. A separatorthat can retain large amounts of organic electrolytic solution may beused in lithium-ion polymer batteries. These separators may bemanufactured by the following exemplary method.

A polymer resin, a filler and a solvent are mixed to prepare a separatorcomposition. The separator composition is coated directly on theelectrode, and then dried to form a separator film. Alternatively, theseparator composition can be cast onto a separate support and dried toform a separator film, which film is then detached from the separatesupport and laminated on an electrode, thereby forming a separator film.

Any polymer resin commonly used in lithium batteries can be used in theseparator. Nonlimiting examples of suitable polymer resins includevinylidenefluoride/hexafluoropropylene copolymers,polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate andmixtures thereof.

The electrolyte may include a lithium salt dissolved in the electrolytesolvent. Nonlimiting examples of suitable electrolyte solvents includepropylene carbonate, ethylene carbonate, diethyl carbonate, ethylmethylcarbonate, methylpropyl carbonate, butylene carbonate, benzonitrile,acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran,gamma-butyrolactone, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethyl acetamide, dimethylsulfoxide, dioxane,1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene,nitrobenzene, dimethyl carbonate, methylethyl carbonate, diethylcarbonate, methylpropyl carbonate, methylisopropyl carbonate,ethylpropyl carbonate, dipropyl carbonate, dibutyl carbonate, diethyleneglycol, dimethyl ether, and mixtures thereof. Nonlimiting examples ofsuitable lithium salts include LiPF₆, LiBF₄, LiSbF₆, LiAsF₆, LiClO₄,LiCF₃SO₃, Li(CF₃SO₂)₂N, LiC₄F₉SO₃, LiSbF₆, LiAlO₄, LiAlCl₄,LiN(C_(x)F_(2x+1)SO₂)(C_(y)F_(2y+1)SO₂) (where each of x and y is anatural number), and mixtures thereof.

The separator is positioned between the cathode electrode and the anodeelectrode to form the electrode assembly. The electrode assembly iswound or folded and then sealed in a cylindrical or rectangular batterycase. Then, the electrolyte solution is injected into the battery caseto complete preparation of a lithium ion battery.

Alternatively, a plurality of electrode assemblies may be stacked in abi-cell structure and impregnated with an organic electrolyte solution.The resultant product is put into a pouch and hermetically sealed,thereby completing a lithium ion polymer battery.

Still another embodiment of the present invention provides a method ofpreparing an anode active material. The method includes sinteringhydrogen silsesquioxane (HSQ) in an inert atmosphere at a temperatureranging from about 900 to about 1300° C. The HSQ preferably has at leastone structure selected from a structures represented by Formulae (2) and(3) and composite structures thereof.

In Formulae (2) and (3), R represents a hydrogen atom.

In an alternative embodiment of the present invention, the HSQ isobtained by subjecting the silane compound represented by Formula (1) toa sol-gel reaction in the presence of catalyst.HSi(R₁)(R₂)(R₃)  (1)In Formula (1), each of R₁, R₂ and R₃ is independently selected fromhalogen atoms, and substituted and unsubstituted C₁₋₁₀ alkoxy groups.Nonlimiting examples of suitable silane compounds includetrichlorosilane, trimethoxy silane, and triethoxy silane. Thesubstituted alkoxy group may include a substituent selected from C₁₋₅alkyl groups, C₂₋₅ alkenyl groups, and C₁₋₅ alkoxy groups.

According to an embodiment of the present invention, in the sol-gelreaction carried out for preparation of the HSQ, from about 10 to about60 wt % of a carbonaceous material (based on the total weight of themixture of the silane compound and the carbonaceous material) is sol-gelreacted with the silane compound. If the carbonaceous material ispresent in an amount less than about 10 wt %, the amount of carboncontained in the anode active material is too small making it theaddition of the carbonaceous material meaningless to the reactionsystem. If the carbonaceous material is present in an amount greaterthan about 60 wt %, the excess of carbonaceous material may give rise toreductions in energy density. Nonlimiting examples of suitablecarbonaceous materials include carbon black, graphite fine particles,amorphous carbon, carbon nanotubes, carbon nanofibers, and vapor-growncarbon fibers.

Alternatively, in the sintering of the HSQ, from about 10 to about 90 wt% of a carbon precursor may be added to the HSQ based on a total weightof the mixture of the HSQ and the carbon precursor. If the carbonprecursor is added in an amount greater than about 90 wt %, energydensity is undesirably reduced. If the carbon precursor is added in anamount less than about 10 wt %, the amount of carbon remaining aftercarbonization is too small to exhibit a meaningful effect. Nonlimitingexamples of suitable carbon precursors include petroleum pitch, coal tarpitch, sucrose, phenol resins, epoxy resins, furfuryl alcohol, polyvinylchloride, polyvinyl alcohol, and the like.

The present invention will now be described with reference to thefollowing examples. However, these examples are presented forillustrative purposes only and are not intended to limit the scope ofthe present invention.

Preparation of Silicon Oxide

EXAMPLE 1

1.5 g of triethoxy silane was added to 10 ml of ethanol and agitated for30 minutes. 0.6 g of 0.5 M HCl solution was added to the resultantproduct and again agitated for 6 hours. After agitating, the resultantsolution was allowed to stand undisturbed by external air at roomtemperature for 2 days until the solution was gelled.

Subsequently, the gelled solution was allowed to stand undisturbed in anoven maintained at about 80° C. for 2 days to evaporate ethanol andmoisture, yielding white powder. The white powder was sintered under aflow of argon gas at a flow rate of 100 ml/min at about 900° C. for 1hour, thereby preparing a silicon oxide (SiO_(x)).

EXAMPLE 2

1 g of the silicon oxide powder prepared as in Example 1 and 0.4 g ofpetroleum pitch (Mitsubishi Chemical Co., Ltd., softening point: 250°C.) were added to 20 ml of THF (tetrahydrofuran), followed by agitatingfor 30 minutes. Subsequently, the resultant solution was continuouslyagitated to evaporate THF, yielding powder. The resultant powder wasfired under a flow of argon gas at a flow rate of 100 ml/min at about900° C. for 1 hour, thereby preparing a silicon oxide coated with acarbonaceous material.

EXAMPLE 3

A SiO_(x)-graphite composite was prepared generally as in Example 1except that 1.5 g of triethoxy silane was added to 10 ml of ethanol and0.6 g of graphite powder (SFG-6 from Timcal Ltd.) was further addedthereto, followed by agitating for 30 minutes.

COMPARATIVE EXAMPLE 1

A silicon oxide (SiO) commercially available from Japan Pure ChemicalCompany Ltd. was used.

COMPARATIVE EXAMPLE 2

A silicon oxide coated with a carbonaceous material was prepared as inExample 2 except that the silicon oxide (SiO) of Comparative Example 1was used, instead of the silicon oxide (SiO_(x)) prepared in Example 1.

XRD (X-Ray Diffraction) Measurement

The structure of the amorphous silicon oxide (SiO_(x)) prepared inExample 1 was analyzed by XRD. The XRD results are shown in FIG. 1. Asconfirmed from FIG. 1, the XRD results indicated that the amorphoussilicon oxide (SiO_(x)) prepared in Example 1 was amorphous.

XPS (X-Ray Photoelectron Spectrum) Measurement

XPS measurements were performed on the amorphous silicon oxide (SiO_(x))prepared in Example 1 and the silicon oxide (SiO) prepared inComparative Example 1. The equipment used for the XPS measurement wasModel No. Q2000 of PHI XPS Systems. The XPS measurement was carried outwith an X-ray source providing monochromatic Al Kα X-ray radiation withan energy of 1486.6 eV, 100 m. The XPS results are shown in Table 1below and in FIG. 2.

TABLE 1 Sample Si2p(2)- Si2p(3)- Si2p(4)- Si2p(1)-99.2 eV 100.8 eV 103.0eV 105.4 eV Comparative 6.6% 2.12% 23.35% 2.1% Example 1 Example 1 1.5%1.08% 16.64% 10.8%

As shown in Table 1 and FIG. 2, the atomic percentage (atomic %) of theamorphous silicon oxide (SiO_(x)) prepared in Example 1, obtained from apeak (4) of Si observed at 105.4 eV, was greater than 10%, while theatomic % of the silicon oxide (SiO) of Comparative Example 1 was lessthan 3%.

The amorphous silicon oxide (SiO_(x)) prepared in Example 1 had arelatively high Si atomic %, which is presumably because of its nanoporestructure.

In FIG. 2, the peak (1) indicates an elemental silicon peak, the peak(3) indicates a SiO₂ peak, and the peak (2) indicates anon-stoichiometric silicon oxide.

Preparation of Anode

EXAMPLE 4

The amorphous silicon oxide prepared according to Example 1, carbonblack (Super-P from Timcal, Inc.), and vinylidene fluoride (PVdF) weremixed in a weight ratio of 75:15:10 with 1 mL NMP to prepare a slurry.The slurry was coated on a Cu foil collector to a thickness of about 50μm using a doctor blade. The resultant Cu foil coated with the slurrywas dried in vacuum at 120° C. for 2 hours, thereby preparing an anode.

EXAMPLE 5

An anode was prepared as in Example 4 except that the silicon oxideprepared according to Example 2 was used instead of the silicon oxideprepared according to Example 1.

EXAMPLE 6

An anode was prepared as in Example 4 except that the silicon oxideprepared according to Example 3 was used instead of the silicon oxideprepared according to Example 1.

COMPARATIVE EXAMPLE 3

An anode was prepared as in Example 4 except that the silicon oxideprepared according to Comparative Example 1 was used instead of thesilicon oxide prepared according to Example 1.

COMPARATIVE EXAMPLE 4

An anode was prepared as in Example 4 except that the silicon oxideprepared according to Comparative Example 2 was used instead of thesilicon oxide prepared according to Example 1.

Preparation of Lithium Battery

EXAMPLE 7

A CR2016-standard coin cell was manufactured using the anode plateprepared according to Example 4, a counter electrode made of lithiummetal, a PTFE separator (Cellgard 3510), and an electrolyte solutionincluding 1.3 M LiPF₆ dissolved in a mixture of EC (ethylene carbonate)and DEC (diethyl carbonate) (3:7 by volume ratio).

EXAMPLE 8

A CR2016-standard coin cell lithium battery was manufactured as inExample 7 except that anode plate prepared according to Example 5 wasused instead of the anode plate prepared according to Example 4.

EXAMPLE 9

A CR2016-standard coin cell lithium battery was manufactured as inExample 7 except that anode plate prepared according to Example 6 wasused instead of the anode plate prepared according to Example 4.

COMPARATIVE EXAMPLE 5

A CR2016-standard coin cell lithium battery was manufactured as inExample 7 except that anode plate prepared according to ComparativeExample 3 was used instead of the anode plate prepared according toExample 4.

COMPARATIVE EXAMPLE 6

A CR2016-standard coin cell lithium battery was manufactured as inExample 7 except that anode plate prepared according to ComparativeExample 4 was used instead of the anode plate prepared according toExample 4.

Charge-Discharge Test

The coin cells prepared according to Examples 7 through 9 andComparative Examples 5 and 6 were charged with a constant current of 100mA with respect to 1 g of anode active materials to a cut-off voltage of0.001 V (vs. Li), and a constant-voltage discharge was performed to acurrent of 5 mA with respect to 1 g of anode active materials whilemaintaining the 0.001 V potential. After a 30 minute rest time, thecharged cells were discharged with a constant current of 50 mA withrespect to 1 g of anode active materials until an endpoint voltage of1.5 V was reached, thereby obtaining a discharge capacity. Thecharge-discharge tests were repeated for 50 cycles. The dischargecapacity at each cycle was measured and a capacity retention rate wascalculated using the measured discharge capacity. The capacity retentionrate was calculated using Equation (1).Capacity retention ratio (%)=(Discharge capacity at 30^(th)cycle/Discharge capacity at 1^(st) cycle)×100   Equation (1)

The results of the charge-discharge cycle tests for the coin cellsprepared according to Examples 7 through 9 and Comparative Examples 5and 6 are shown in Table 2 and in FIGS. 3A and 3B.

TABLE 2 1st cycle discharge 30th cycle discharge Capacity capacitycapacity retention Coin Cell (mAh/g) (mAh/g) ratio (%) Example 7 516 9919.3 Example 8 905 546 60 Example 9 736 477 64.8 Comparative 393 35 9Example 5 Comparative 427 26 6.1 Example 6

As shown in FIGS. 3A and 3B, the coin cell using the amorphous siliconoxide prepared according to Example 7 (FIG. 3A) had substantially thesame lithium intercalating capacity as the coin cell using the siliconoxide prepared according to Comparative Example 1 (FIG. 3B). However,the coin cell using the amorphous silicon oxide prepared according toExample 7 had a noticeably increased reversible lithium deintercalatingcapacity.

In addition, as shown in Table 2, the capacity retention ratios of thecoin cells prepared according to Examples 7 through 9 were noticeablyincreased compared to those of the coin cells prepared according toComparative Examples 5 and 6.

These results indicate that charge and cycle life characteristics of abattery can be noticeably improved when an anode active materialaccording an embodiment of the present invention is used. As confirmedfrom the XPS experiment results, the amorphous silicon oxides (SiO_(x))of the present invention have nanopore structures, and atomic %s of Sigreater than 10%, yielding having high binding energies, leading toexcellent lithium ion intercalation/deintercalation characteristics.

Unlike in methods of preparing conventional silicon oxides, whichrequire sintering at high temperatures of 1200° C. or higher and rapidcooling, the anode active materials according to the present inventioncan be simply prepared by sintering under an inert atmosphere.

The inventive anode active materials are composite anode activematerials containing novel amorphous silicon oxides directly obtained bysintering hydrogen silsesquioxane (HSQ). Anodes and lithium batteriesincluding such anode active materials exhibit improved charge anddischarge characteristics.

While the present invention has been illustrated and described withreference to certain exemplary embodiments, it is understood by those ofordinary skill in the art that various changes and modifications may bemade to the described embodiments without departing from the spirit andscope of the present invention as defined by the following claims.

1. A silicon oxide based composite anode active material comprising anamorphous silicon oxide represented by SiO_(x), wherein 0<x<2, theamorphous silicon oxide having a binding energy ranging from about 103to about 106 eV and a silicon peak with a full width at half maximum(FWHM) ranging from about 1.6 to about 2.4 as measured by X-rayphotoelectron spectrometry, wherein the amorphous silicon oxide has anatomic percentage of Si calculated from an area of the silicon peak ofgreater than or equal to about
 8. 2. The silicon oxide based compositeanode active material of claim 1, wherein the amorphous silicon oxidehas a binding energy ranging from about 105 to about 106 eV.
 3. Thesilicon oxide based composite anode active material of claim 1, wherein1<x<1.7.
 4. The silicon oxide based composite anode active material ofclaim 1, wherein the amorphous silicon oxide has an atomic percentage ofSi, calculated from an area of the silicon peak, of greater than orequal to about
 10. 5. The silicon oxide based composite anode activematerial of claim 1, wherein the amorphous silicon oxide has an atomicpercentage of Si, calculated from an area of the silicon peak, rangingfrom about 8 to about 10.8%.
 6. The silicon oxide based composite anodeactive material of claim 1, further comprising carbonaceous particlesdispersed in the amorphous silicon oxide.
 7. The silicon oxide basedcomposite anode active material of claim 1, further comprising acarbonaceous coating layer on the amorphous silicon oxide.
 8. An anodecomprising a silicon oxide based composite anode active materialcomprising an amorphous silicon oxide represented by SiO_(x), wherein0<x<2, the amorphous silicon oxide having a binding energy ranging fromabout 103 to about 106 eV and a silicon peak with a full width at halfmaximum (FWHM) ranging from about 1.6 to about 2.4 as measured by X-rayphotoelectron spectrometry, wherein the amorphous silicon oxide has anatomic percentage of Si calculated from an area of the silicon peak ofgreater than or equal to about
 8. 9. A lithium battery comprising theanode of claim 8.